1. Field of the Invention
The present invention relates generally to cycle timers, and specifically to a cycle timer which activates a household appliance at a preset time of day.
2. Description of the Background Art
For automatic activation of household appliances such as coffee makers, cycle timers have been used which generate an activation signal at a preset time each day. The cycle timers have used either mechanical gear trains or electronic counting circuits to keep track of the time of day, and cam switches or numerical comparator circuits to generate the activation signal.
Typically the cycle timer has a switch with three positions, including an "ON" position, an "AUTO" position, and an "OFF" position. In the "AUTO" position, the cycle timer typically generates an activation signal having a duration of about 105 to 135 minutes starting when the time of day reaches the preset time. Electronic timers of this kind are described in U.S. Pat. Nos. 4,697,930 to Roberts et al. and 4,566,802 to Koehler.
Koehler U.S. Pat. No. 4,566,802 is specifically directed to the use of a bistable circuit for preventing an activation signal from being generated on a daily basis without manual intervention. For automatic coffee makers, such a "lockout" feature may prevent a fire from occurring, since repeated operation of the coffee maker with an empty water reservoir increases the likelihood of a fire.
In Koehler, the bistable circuit is set to activate an activation enable signal upon receipt of the cycle enable signal, and is reset by the activation signal to disable the activation enable signal. For a coffee maker, the bistable circuit is preferably reset by the activation signal at the active-to-inactive transition signalling the end of brewing. Preferably the bistable circuit is set by the "OFF" position of the three-position switch. Such a bistable circuit has been incorporated onto the same integrated circuit as the electronic counters for registering the time of day. In this case a "lockout" flip-flop has been used for the bistable circuit.
At one time the electronic cycle timer, with an LED or fluorescent digital display, was the most popular. Recently, however, analog display timers have come back in fashion. But consumers expect to have the same quality and features that are found in the electronic timers, such as twenty-four hour cycles instead of twelve-hour cycles. In response, manufacturers have offered improved mechanical movements. A mechanical movement has been introduced, for example, having a cam-operated switch to turn on a household appliance at a preset time of day and an automatic shut-off in which a cam mechanically moves the three-position manual switch from the automatic to the off position after a certain activation interval. Such a mechanism is disclosed in Wingler et al. U.S. Pat. No. 4,695,683. Such mechanisms, however, are subject to wear and variations in their timing intervals.
One successful attempt to improve the analog display timers involves the use of a quartz crystal, electronic oscillator and counter, and low-RPM synchronous motor. One such popular "quartz movement" is manufactured by Ikeda Bussan, Ltd. (New Tokyo Bldg. #3/1, Muranouchi 3-Chome, Chiyoda-Ku, Tokyo 100, Japan). Similar clock movements are offered by other manufacturers. The movement is virtually noiseless and very durable. Although the mechanism was originally designed to be battery powered and has low-voltage, low current switch contacts, it has been used as an appliance timer by the addition of a line-voltage driven power supply and a relay activated by the low-current switch contacts via a transistor current amplifier. Such a "hybrid" electronic and mechanical timer, however, is relatively expensive due to the cost of the quartz crystal. In addition, the timer does not have a "lockout" mechanism, and the duration of the activation interval is relatively imprecise.